The present invention pertains to polymeric thiosynergists, such as poly[2-(ethylthio)ethyl methacrylate], and to compositions which are stabilized by these materials against the deleterious effects of heat and oxygen.
Of particular interest are polyolefin resin compositions containing said derivatives which are stabilized against thermal aging and light induced degradation. Polyolefin resins have inherently good mechanical and physical properties and are useful as resin substrates for molded articles, films and fibers. Other resins of particular interest include thermoplastic elastomers, ABS resins, polystyrene, and other hydrocarbon polymers.
In an attempt to permit these resins to exhibit the full measure of their inherent properties, it has been customary to add one or more stabilizers to the resins to overcome their susceptibility to oxidative and thermal degradation.
Phenolic antioxidants have long been used in the art as such stabilizers with varying degrees of success as seen in U.S. Pat. No. 3,285,855. It was shown in U.S. Pat. No. 2,956,982 that the dialkyl esters of .beta.-thiodipropionic acid were also effective stabilizers for polyolefin resins. The combination of a lesser amount of a phenolic antioxidant with a small quantity of a dialkyl .beta.-thiodipropionate was found to have a synergistic effect on the level of stabilization of such compositions superior to the use of either the phenolic antioxidant alone or the dialkyl .beta.-thiodipropionate alone at the given concentration, (U.S. Pat. No. 3,285,855).
Other sulfur containing compounds have been discovered which also exhibit synergistic stabilization effects in combination with phenolic antioxidants in polyolefin compositions. These include the dialkyl alkylthiosuccinates (U.S. Pat. No. 3,345,327); the thiodialkanoate polyesters (U.S. Pat. Nos. 3,157,517 and 3,378,516); the derivatives of N',N",N'"-tris(3-mercaptopropionyl)hexahydros-triazine (U.S. Pat. No. 3,538,092); the pentaerythritol or trimethylolpropane esters of alkylthioalkanoic acids (U.S. Pat. Nos. 3,629,194 and 3,758,549); the 2,4,6-tris-(alkylthioalkylthio)-1,3,5-triazines (U.S. Pat. No. 3,652,561); and the tris(2-alkylthioalkanoylethyl) isocyanurates (Japanese Kokai 75/106,881).
While all of these materials exhibit useful synergistic stabilization effects in the presence of phenolic antioxidants in polyolefin or other hydrocarbon systems which are subject to oxidative and/or thermal deterioration, the dialkyl .beta.-thiodipropionates (particularly the dilauryl and especially the distearyl esters) have become the thiosynergists of choice in the art enjoying widespread use.
Alkylthioalkyl acrylate, methacrylate and crotonate monomers are widely known. These polymerizable monomers have been used with a variety of other vinyl monomers to prepare copolymers having a plethora of uses such as in flocculents (U.S. Pat. No. 3,280,081), property improvement additives for paper (U.S. Pat. Nos. 3,207,656; 3,332,835), flame resistant acrylic sheet (U.S. Pat. No. 3,634,554), acrylic elastomers (German Offen No. 2,025,342) and viscosity index improvers for oils (U.S. Pat. Nos. 3,278,500; 3,354,087).
Copolymers of methyl methacrylate with 0.1 to 10% .beta.-(ethylthio)ethyl methacrylate were found to be more resistant to thermal oxidative degradation than either homopolymer of the above monomers. (USSR 300,482; A. A. Berlin et al, Vysokomol Soedin, A14(4), 860 (1972).
The homopolymers of alkylthioalkyl methacrylates are also known. Poly[.beta.-(ethylthio)ethyl methacrylate] was described by Berlin supra and its synthesis and polymerization characteristics by S. Hashimoto et al, Kobunshi Kagaku, 27(298) 110 (1970); Chem. Abst., 73, 4225 g (1970).
Poly[.beta.-(ethylthio)ethyl methacrylate] has been used as a catalyst in preparing .beta.-hydroxyalkyl esters useful in coatings (South Africa Pat. No. 68 01,333) and has been reacted to form a polymeric structure with pendant sulfonium groups useful in adhesives, coatings and finishes (U.S. Pat. No. 3,310,540).
Poly[.beta.-(dodecylthio)ethyl methacrylate] was found useful as a viscosity index improver and antisludge additive in turbine fluids (U.S. Pat. No. 3,269,808).
The use of poly(alkylthioalkyl methacrylates, acrylates and crotonates) as polymeric thiosynergists in polymer compositions stabilized against oxidative, thermal and/or light induced deterioration is not disclosed or suggested in the prior art.
Polymeric stabilizers consisting of acrylic or methacrylic acid copolymers with styrene, ethylene or methyl methacrylate esterified with the glycidol esters of alkylthiopropionic acid are disclosed in Japan 69 32,056. These structures are only remotely related to the instant homopolymers.